1. Field of the Invention
The present invention relates to a projector constructed so as to be able to modulate light emitted from a light source including light emitting diodes and to project and display an image on a screen.
2. Description of the Related Art
To reduce power consumption and apparatus size, a projector that uses high-intensity light emitting diodes (LEDs) as a light source in place of a light source such as a high-pressure mercury lamp has been proposed. As one example of this type of projector, Japanese Laid-Open Patent Publication No. 2002-244211 discloses an image projecting apparatus equipped with LED light sources including a plurality of LEDs. In this case, one LED light source is formed of a plurality of blue LEDs so as to be capable of emitting blue light, one LED light source is formed of a plurality of green LEDs so as to be capable of emitting green light, and one LED light source is formed of a plurality of red LEDs so as to be capable of emitting red light. In this image projecting apparatus, the respective LED light sources are alternately lit in order to emit blue light, green light, and red light in order, and a single-panel light modulating method is used to modulate the blue light, green light, and red light using a liquid crystal light valve in synchronization with the timing with which the LED light sources are alternately lit.
More specifically, when one LED light source is lit, the blue light emitted from the LED light source is polarized by a polarizing conversion element, and is then reflected by a dichroic prism and a polarizing beam splitter and is shone towards a reflective liquid crystal light valve. At this time, the blue light that has been modulated by the liquid crystal light valve (i.e., the modulated blue light) passes a polarizing beam splitter and is projected towards a screen by a projection lens. Similarly, when another LED light source is lit, the green light emitted from the LED light source is polarized by the polarizing conversion element, and is then reflected by a dichroic prism and a polarizing beam splitter and is shone towards a reflective liquid crystal light valve. At this time, the green light that has been modulated by the liquid crystal light valve (i.e., the modulated green light) passes a polarizing beam splitter and is projected towards a screen by a projection lens. Additionally, when yet another LED light source is lit, the red light emitted from the LED light source is polarized by the polarizing conversion element, and is then reflected by a dichroic prism and a polarizing beam splitter and is shone towards a reflective liquid crystal light valve. At this time, the red light that has been modulated by the liquid crystal light valve (i.e., the modulated red light) passes a polarizing beam splitter and is projected towards a screen by a projection lens. In this way, by repeatedly carrying out a process of alternately lighting the LED light sources and modulating the light using a liquid crystal light valve with an extremely short cycle, it is possible to project and display a color display image on a screen.
However, by investigating the image projecting apparatus described above, the present inventor discovered the following problem. That is, in this image projecting apparatus, the LED light sources are respectively composed of the same number of LEDs, and blue light, green light, and red light are emitted in order by alternately lighting these LED light sources. In this case, to project and display the display image on the screen with natural tones (in a state where the white balance has been adjusted), it is necessary to set the ratio between the blue light, the green light, and the red light incident on the liquid crystal light valve at 1:6:3, for example. Also, the luminance (luminous efficiency) respectively differs when red LEDs, green LEDs, and blue LEDs are supplied with currents of equal value. Accordingly, in order to have blue light, green light, and red light emitted from LED light sources equipped with equal numbers of LEDs with respectively different luminances so that the ratio of colored light is 1:6:3, it is necessary to reduce the current supplied to the high luminance LEDs in accordance with the low luminance LEDs so as to reduce the luminance. As a result, since conventional image projecting apparatuses are equipped with equal numbers of high luminance LEDs and low luminance LEDs regardless of the supplied current being reduced to reduce the luminance, there is the problem that the manufacturing cost of such apparatuses is high.